Multiple Charging Circuits

I returned to the boat with a new fuse for the bow thruster circuit. Once connected I measured the voltage at the bow thruster with the Travelpower providing 240ac to the Victron Multiplus inverter/charger. All is well there. Further tests at the domestic battery bank revealed the domestic alternator was not supplying any current.Time for a bit more wire tracing. With the help of the Beta Marine engine manual I found the cable that normally connects the domestic alternator D+ terminal had been cut at the engine end. This meant that the alternator will not start supplying current until it reaches quite high revs.
Alternator fact: The alternator only needs a current to energise it at low revs. At high revs the weak magnetic field already present in the rotor will generate enough current to energise the alternator.
I think it was disconnected to avoid having the alternator and Victron compete to charge the batteries. I'm going to reconnect it because the domestic alternator is essential for recharging while cruising when the Travelpower is not running. The two charging systems will only compete in as much as the one with the lowest voltage output will shut down and leave the field clear for the other. I'd rather have the two systems running than none at all as we had when the Travelpower drive belt broke.

Things that Go Pop

After two weeks of battery-pampering I returned the batteries to Syncopation. There were five to refit: four domestic and one bow-thruster. I put the bow-thruster back in first and then got to work trimming the side of the battery box to make replacing the domestic batteries easier. Twenty minutes later I had all the batteries in and began connecting them. I connected the cable from the bow thruster battery to the first in the domestic bank and was surprised by a fat spark. When I touched the terminal with the cable again there was a bigger spark and the nearby fuse blew. Oops! A quick check revealed I had put the bow thruster back in back to front, so the 175 Amp fuse protecting the bt battery charging cable blew when I completed the circuit.

When everything was connected I started the engine and checked the battery voltage and found as I suspected that the domestic alternator was supplying no charge. I switched on the Travelpower and fired up the Victron Multiplus and found a healthy charge going into the batteries.

A check of the instrument panel revealed no red light on starting the engine for the domestic alternator so I traced the cable from the back of the panel. The loose cable looked suspicious and proved to be the connection from the alternator to the charge light - so no charge. It was easy to fix - just plug it in - and the domestic alternator was still not charging. Further investigation required I think.